The present invention relates generally to pump devices having two pumps arranged in parallel in the direction of a motor output shaft, and more particularly, to the pump devices applied to brake systems for motor vehicles with anti-lock brake control and cruising stabilizing control such as traction control or yaw-rate feedback control.
Conventionally, pump devices having two pumps arranged in parallel in the direction of a motor output shaft have been proposed to carry out anti-lock brake control, etc. One of the pump devices is known, for example, in JP-A 64-77767. This pump device includes eccentric parts arranged along a motor output shaft on the pointed-end side and on the base-end side, needle roller bearings arranged on the outer peripheries of the eccentric parts, and pairs of plungers arranged to abut on the outer peripheries of the bearings. Note that anti-lock brake control is effective when a master-cylinder pressure is produced by brake operation carried out by a driver.
Recently proposed are brake systems in which when a driver does not depress a brake, i.e., no master-cylinder pressure is produced, a wheel-cylinder pressure is produced to obtain a braking force by which cruising stabilizing control such as traction control or yaw-rate control is carried out. Production of the wheel-cylinder pressure when no master-cylinder pressure is produced needs immediate production or rise of a brake-fluid pressure. The use of a pump with a capacity enough for immediate production of the brake-fluid pressure results in wasteful energy consumption since the capacity is too large for anti-lock brake control, and in an increase in weight, installation space, and manufacturing cost.
For solving such problems, a brake system is proposed including main and auxiliary pumps arranged in parallel, wherein the main pump has a capacity necessary for anti-lock brake control, and the auxiliary pump serves to supply brake fluid to the inlet of the main pump upon cruising stabilizing control to ensure a pump capacity enough for cruising stabilizing control. The use of the pump device disclosed in JP-A 64-77767 for that purpose is advantageous in view of installation space, weight, and manufacturing cost.
However, the pump device disclosed in JP-A 64-77767 has the following inconveniences since the eccentric parts have substantially the same outer diameter:
The bearing is press fitted to the outer periphery of each eccentric part. When press fitted to the base-end side or second eccentric part, the bearing should pass over the pointed-end side or first eccentric part, which is impossible, however, when the motor output shaft is integrated with the eccentric parts since the eccentric parts have substantially the same outer diameter. Therefore, a shank or eccentric member having each eccentric portion arranged is formed separately from the motor output shaft, and the bearings are press fitted to the eccentric member from both ends. Moreover, connecting members are needed to connect the eccentric parts and the motor output shaft. Those result in complicated structure due to increase in the number of component parts, and increased manufacturing cost.
On the other hand, in case of applying the pump device to the brake system with anti-lock brake control and cruising stabilizing control, smooth supply of brake fluid to the main pump is obtained only if the auxiliary pump is in the discharge stroke when the main pump in the suction stroke, which requires driving of the plungers of the main and auxiliary pumps with phase shifted. With the pump device including the first and second eccentric parts having substantially the same outer diameter as disclosed in JP-A 64-77767, formation of the shapes of the first and second eccentric parts with different phases consumes time, and integration of the first and second eccentric parts with the motor output shaft is difficult to be done. Moreover, amounting of two bearings to the motor output shaft from one direction becomes more difficult.
It is, therefore, an object of the present invention to provide pump devices which contribute to a reduction in component parts and manufacturing cost with excellent work efficiency, and enable easy formation of first and second eccentric parts with different phases.